This invention relates to manhole cover and frame assemblies and, in particular, to an inner frame member or insert for raising the level of a manhole cover upon resurfacing a roadway.
Manhole cover and frame assemblies located along a roadway typically include an outer frame having a seat on which a manhole cover rests flush with the roadway surface. Ordinarily, a manhole cover support insert is used when the roadway is resurfaced with an added layer of paving material. The support insert raises the level of the manhole cover to the new street level. Support inserts typically occupy the seat where the manhole cover was intended to rest in the outer frame. Manhole frame and cover assemblies may be provided with a locking mechanism to prevent unauthorized personnel from removing the cover.
Manhole assemblies are currently unable to satisfactorily prevent "inflow", a combination of storm water and other street surface liquids, from entering an access opening of the outer frame. This inflow may consist of billions upon billions of gallons of excess street surface liquids. Once the inflow enters the manhole frame it gains entry into utility services such as sanitary sewer distribution lines, where it burdens wastewater treatment plants, and gas, electric or telecommunications underground vaults. The inflow is a problem because it mixes with the effluent in sanitary sewers, resulting in costly additional wastewater treatment.
An additional problem is presented when the inflow reaches other utility service areas normally found in gas, electric or telecommunications distribution lines. These service areas have concrete manhole casements that do not have an individual drainage system, and thus are partially or completely filled with inflow. Such installations often require extensive vacuum pumping to remove the inflow before workmen can safely enter the manhole to perform the required maintenance or other utility service.
Manhole frame and cover casting assemblies are normally comprised of metal castings, generally produced by cast iron foundries, using sand casting molds. These casting methods are used to produce manhole components in cast ductile iron, grey cast iron, or the like. Castings made from these casting processes create difficulties in duplicating nearly exact castings as compared to the mold images. Non-uniform shrinkage, warpage, and the like promote dimensional instability that affects the fit between metal surfaces necessary to provide a water-tight condition.